This invention relates generally to methods for manufacturing rods formed of electrically insulating plastic material, and more particularly, to a method for manufacturing a fiber-reinforced, hollow-cylindrical push or pull rod formed of electrically insulating material and having flange fittings fastened at end faces thereof for transmitting compression or tension forces; the fibers being formed of threads which are oriented parallel to the axis of the rod and are impregnated with hardenable plastic material.
Push or pull rods formed of insulating material are used as force-transmitting members in high voltage circuit breakers. In such circuit breakers, the contacts across the switching gaps are at high voltage potentials, and are actuated by a drive at ground potential. One particular hollow, cylindrical push or pull rod which is known is described in DE-AS No. 24 29 475. In this known rod, sleeves are provided in the vicinity of the end faces as force transmitting members which cover the areas of the tube wall of the rod at the end faces. The sleeves are connected by a close fit to the rod by elements of structure which are inserted into the outer layer of the rod, project radially beyond the tube wall, and engage in recesses in the sleeves. This known push or pull rod is made by a process essentially in which a fabric having threads oriented parallel and transversely to the axis of the rod is impregnated with electrically insulating plastic material of the type which is hardenable. The wrapping process may be of a wet type, or a dry wrapping process wherein the wrap is subsequently impregnated.
It is a problem with such known rods that even if high tensile strength threads are used, the rod can be stressed in compression or tension only to the extent that the form-locking connection between the sleeve and the outer layer of the rod can be stressed in shear. It is, therefore, an object of this invention to provide a method for manufacturing a fiber-reinforced push or pull rod wherein the tensile strength of the rod is relatively large and limited essentially by the tensile strength of the threads which are oriented parallel with the axis of the rod.